1. Field of the Invention
The present invention relates to a digital camera provided with a perspective correction function and, more particularly, relates to a digital camera provided with a mechanical perspective correction mechanism.
2. Description of the Related Art
In the case where buildings such as a high-rise building or the like is photographed by a camera which is not provided with a shifting mechanism and a tilting mechanism of an imaging lens, it is usually photographed at an angle looking up at the buildings; and it becomes a perspective image in which the more upward vertical lines other than the screen center are, the closer the vertical lines get to the center side. In architecture photographs, deformation of a photographic subject due to such perspective is not preferable; and as photographing materials which can correct perspective for architecture photographs, there are a large-format view camera capable of freely shifting and tilting a photographing lens and an interchangeable lens for a single-lens reflex camera provided with a shifting mechanism and a tilting mechanism; however, there is a problem in that a device itself is large and price is costly.
In a digital image process field, there is provided application software which can freely modify an image; and if a portion that dwindles in a tapered shape toward on a digital image photographed by a digital camera is enlarged in a horizontal direction and a vertical length is adjusted by a perspective correction command of this kind of application software, an architecture photograph similar to an image photographed by a camera provided with the shifting mechanism and the tilting mechanism can be made.
However, a correction process such as magnification by application software is performed by scanning line magnification and an image interpolation process like digital zoom; therefore, deterioration of image quality is inevitable. In addition, image data photographed by a digital camera is usually compressed by nonreversible compression algorithm such as the joint photographic experts group (referred to as JPEG); therefore, there is a problem in that image quality deteriorates for each storage of data by performing the correction process.
A digital camera disclosed in Japanese Patent Application Laid-Open No. 2002-335438 is known as one which reduces a problem of such image quality deterioration to some degree. This digital camera incorporates a processor which can perform perspective correction with respect to image data output by an image pickup device, can reduce deterioration of image quality by performing perspective correction at a stage before data compression and storage, and can confirm a state of the perspective correction by a liquid crystal display (referred to as LCD) display provided in the camera before photographing.
The digital camera disclosed in Japanese Patent Application Laid-Open No. 2002-335438 does not need perspective correction with respect to image data after photographing and reduces trouble of a correction process due to application software and deterioration of image quality due to the correction process; however, a process which gradually enlarges magnification of horizontal scanning lines and magnification in a vertical direction from the bottom side to the upper side of the image and a pixel interpolation process are performed in photographing; therefore, there is a problem that substantial reduction in the number of pixels of the image pickup device generates deterioration of image quality as in digital zoom.
The present applicant has already filed a patent application (Japanese Patent Application No. 2005-233514) of a digital camera provided with a shifting mechanism of an image pickup substrate as a digital camera, which does not need an expensive interchangeable lens or the like provided with a lens shifting mechanism and can suppress deterioration of image quality as much as possible in perspective correction of such digital photographs. This digital camera is provided with a rack and pinion shifting mechanism which can arbitrarily shift an image pickup device in an X direction and a Y direction in a camera body. Accordingly, the perspective correction is performed by shifting the image pickup substrate in the Y direction or X direction while watching an LCD display before photographing; even in a shifting state, the number of effective pixels of the image pickup device is not different from that in anon-shifting state; and deterioration of image quality does not appear.
According to the digital camera (Japanese Patent Application No. 2005-233514) proposed by the present applicant, the perspective correction can be performed without deterioration of image quality; however, in order to keep optical accuracy at high level as a camera, it is required to prevent generation of posture change in the image pickup substrate to be shifted.